Not applicable.
Not Applicable.
Generally, the present invention relates to multimeters, and, more specifically, to multimeters having functions that may be especially useful to those involved in servicing, maintaining, and/or operating electrical power transmission and distribution systems.
Three-phase electrical power is delivered to commercial, industrial, and residential users through a system known as the power distribution grid, which generally includes such components as generating plants, transformers, and electrical power lines. These lines generally consist of both transmission lines, which typically have AC voltages in the range of about 69,000 to 765,000 volts, and distribution lines, which typically have AC voltages in the range of about 2,300 to 50,000 volts. Inevitably, there is an element of danger in measuring and working with these high voltages, yet there are many instances in which utility workers have to either service or repair, or install or interconnect high voltage power lines in the performance of their duties. These duties have been further expanded over the past few years due to the increase of electrical power co-generation by entities that are not part of, or owned by, the electrical power utility that owns and operates the primary power distribution grid. These co-generation entities, however, still connect to the electrical power utility in most cases, and generally do so at the aforementioned high voltage levels.
Generally, therefore, those individuals working with electrical power lines often find it necessary to be able to determine or measure the following parameters: phase-to-phase, phase-to-ground, ground-to-phase, and zero reference test, voltages associated with those lines, which can range from zero volts to full transmission line voltages; the phase rotation or the phase sequence of the three-phase AC lines; and the number of degrees of separation between any two phases. Currently, many different pieces of equipment are used for determining the above-mentioned parameters. As examples, the absolute voltage carried by a line may be measured by a xe2x80x9chigh line resistive voltmeterxe2x80x9d or a xe2x80x9cphasing voltmeter,xe2x80x9d and the phase sequence (or phase rotation) may be determined by using a phase sequence indicator (or a phase rotation meter) prior to connecting individual lines of multi-phase networks together.
Presently, high-voltage phasing voltmeters use a series connected meter, two test probes, which are basically high-voltage dropping resistors that are housed in an insulated holder, and a connection cable, which is used for connecting the second test probe to the other components. The test probes generally have metal hooks or other fittings on their ends for making good electrical contact with the power lines, and often the meter is mounted to one of the two test probes and oriented so that the electric utility worker can read the voltage displayed on the meter while taking a measurement. Additionally, insulated extension poles, commonly referred to as xe2x80x9chot sticksxe2x80x9d may be used to hold and elevate the entire assembly, and in many situations may be required in order to protect the worker from the hazards associated with high-voltage power lines. Generally, the above-mentioned meter may be designed to measure either voltage or current, but, generally, its display will only indicate voltage. One issue when taking AC voltage measurements, however, is the concern that the indicated voltage is not always the true voltage for the four types of voltage measurements listed above. This is especially a concern when taking high-voltage measurements.
High-voltage measurements are plagued with inaccuracies including those stemming from stray capacitive charging currents. At high-voltages, these stray currents emanate from the surface of every component of the measuring device including the connection cable, and other, i.e., additional, currents may be induced by the electromagnetic fields associated with the power lines. The capacitive current is related to the capacitive reactance, Xc, and, depending on the position of the meter and the connection cable with respect to the ground, the magnitude of this impedance can widely range from a very low to a very high value. Under extreme conditions, such as when the connection cable is lying directly on the ground between two pad-mounted transformers, the value of the capacitive reactance can be very low, which can result in the capacitive current equalling or exceeding the measured current and in highly inaccurate meter readings. In other words, it is often the case that the voltage measured by the meter will vary depending on the location of the meter and the cable.
These AC phasing voltmeter inaccuracies, which are generally attributable to capacitive currents, are eliminated in analog and digital devices using an earth ground lead or cable by the design disclosed and described in the commonly owned U.S. patent application Ser. No. 09/766,254, filed on Jan. 18, 2001, which will be referred to herein as xe2x80x9cCompanion Specification 1,xe2x80x9d and are eliminated in digital devices that do not require the use of an earth ground lead or cable in the commonly owned U.S. patent application, Ser. No. 60/327,481, filed on Oct. 5, 2001, which is attached hereto and incorporated in its entirety herein by reference, and which will be referred to herein as xe2x80x9cCompanion Specification 2.xe2x80x9d
Regardless of the above, there are still other problems with standard phasing voltmeters. On occasion, the electrical power transmission lines are separated by a considerable distance and, even though the alternating current phasing voltmeter disclosed in Companion Specification 1 practically eliminates capacitive currents regardless of the length of the cable, it does not effectively address the problem of the logistics involved in dealing with a long cable, or the problem of having a cable that is not long enough. This problem, however, was addressed and eliminated by the design disclosed and described in a commonly owned U.S. patent application Ser. No. 09/814,993, filed Mar. 22, 2001, which will be referred to herein as xe2x80x9cCompanion Specification 3.xe2x80x9d
Other related problems, however, still exist. For example, when measuring very high-voltages there is a difficulty associated with having to use an unwieldy or cumbersome length of dropping resistors and extension pole segments in order to take the high-voltage measurements and/or to determine other electrical parameters. Secondly, due to the hazards associated with the high-voltages being measured, the meter oftentimes has to be kept a considerable distance away from the user. Thirdly, the meter is generally used out of doors during all types of weather and at all times of the day. Because of these constraints, even though accuracy in making the measurements may be accomplished through use of the inventions described in the Companion Specifications, this does not always translate to a user being able to accurately read the meter. In other words, being able to extract the indicated voltage or parameter information is not always easy to do, or can it be done accurately and/or efficiently when using a standard prior art meter.
Thus there remains a need for an alternating current phasing multimeter that can be used without an earth ground lead or cable, can be used over a large range of voltages, can provide other useful information to the user, can be easily and efficiently read, and can be easily used when the power lines are separated by more than a few feet.
According to its major aspects and briefly recited, the present invention is a wireless AC phasing multimeter, which is comprised of an AC phasing voltmeter, preferably having improved accuracy, and may also include a phase sequence or phase rotation indicator, along with a phase comparison indicator. Furthermore, the present invention can be viewed as a modular device having two primary modules: a meter probe module, which is necessary in every embodiment of the invention; and a supplementary probe module, which is not needed to perform the invention in at least one of the embodiments. Generally, the present invention modules can be used as a wireless AC phasing voltmeter having the capability of providing measurements with an improved accuracy and/or providing additional functions not generally found in, or provided by, standard AC phasing voltmeters. In making the above-mentioned determinations and measurements, two modules of the present invention can be attached to and placed in electrical communication with test probes. These probes are used to make an electrical connection to the electrical power lines or conductors, and, in turn, allow the modules to develop a signal associated with each power line parameter of interest. Preferably, from these signals, the present invention may be able to measure many different parameters including, but not limited to, phase-to-phase, phase-to-ground, ground-to-phase, and zero reference test, voltages associated with those lines. Preferably, these signals also allow the present invention to ascertain phase sequence or rotation, as well as the phase difference between the lines being tested. Once the parameters of interest are ascertained by the present invention, the parameters are preferably displayed digitally on the meter probe module""s built-in display, which may be attached to a test probe as described above. However, in another preferred embodiment of the present invention, the meter probe module is not attached to a test probe. Instead, one or two supplementary probe modules are attached, through test probes, to separate power lines and signals are transmitted from each supplementary probe module to a supervisory module (i.e., a meter probe module that is not attached to a test probe and, therefore, may be hand-held) where they are received and displayed by the supervisory module. This is especially useful when working with high-voltage lines in that, for example but not as a limitation, the length of dropping resistors and the insulated extension pole segments needed to drop the voltage to a usable level, i.e., in order to protect the user (e.g., utility worker), can be considerable and unwieldy, and can cause the measuring device to be a considerable distance away from the user. Therefore, the present invention multimeter not only can be applied to power lines that are a considerable distance apart without being limited by a test probe interconnection cable, but the present invention also allows the parameters of the high-voltage power lines being tested to be accurately read by bringing each display and/or indicator closer to the user in these situations while providing the related advantage of eliminating the need for the long, unwieldy, length of dropping resistors and insulated pole segments. The present invention phasing voltmeter multimeter includes a pair of high impedance test probes, each of which is in series with a communication circuit and in series or in communication with circuitry that is used for determining the electrical parameters of interest and displaying the results of such determinations.
The probes and circuitry of the phasing voltmeter multimeter may be shielded, and the shielding may be electrically connected to the components and/or the circuitry of the present invention in order to alleviate the effects of capacitive charging currents. Relatedly, and preferably, the present invention does not require the use of an earth ground lead or cable. However, other embodiments, for example, those used for measuring voltages in the range of 0-25 kV, may be used with an earth ground cable or lead. In addition to the above-mentioned components, signal phase shift compensation may be used to compensate for phase shifts that may occur in the present invention due to radiative transmission and reception of the signals used to determine the parameters of interest. Preferably, this compensation may be accomplished through the use of hardware and/or software within the modules; however, any other suitable method may also be used.
An important feature of the present invention is the use of an electromagnetic radiation communication means for transmitting and receiving the signals. This feature has several advantages. First, it eliminates the cable, which, in addition to the cost and the need to manage and maintain the cable as part of a standard AC phasing voltmeter, also imposes a significant physical limitation on the distance between the two probes. In other words, the present invention allows the taking of voltage, and/or phase sequence, and/or difference measurements between two power (e.g., transmission and/or distribution) lines that may be located very far apart. Third, it reduces the natural trepidation of workers who are making measurements on electrical power lines carrying very large voltages. And, while any electromagnetic waves (visible, infra-red, radio-frequencies, or microwave, for example) can be used, radio frequencies are preferred because they allow for other objects to be in the line-of-sight between the transmitter and the receiver without an appreciable loss of signal. Furthermore, it is preferable that the signals are transmitted digitally and in such a way as to minimize the effects of electrical noise on the transmission, such as by frequency shift keying, but other known transmission methods can be used as well.
Another feature of the present invention is that it is possible to retrofit a standard AC phasing voltmeter with the communication means of the present invention instead of using a connection cable. For example, in one embodiment, supplementary probe modules, i.e., signal transmitters, are attached to the power lines (or electrical test points) of interest and are used to send signals to a supervisory module, i.e., a receiver, which is attached to a standard AC phasing voltmeter.
Still another feature of the present invention is the optional inclusion of wireless signal compensation to eliminate wireless signal errors, which could allow for more accurate readings.
Still another feature of the present invention is the use of modular components, which allows the user more flexibility in the manner in which the measurements are taken and displayed, and which allows for the incorporation of optional features.